4.3 Infectious Diseases
Key Takeaways
Infectious Diseases is 7% of the PANRE blueprint; high-yield areas are common bacterial and viral infections, sepsis recognition, HIV, antimicrobial selection, and immunizations
Sepsis is organ dysfunction from a dysregulated host response to infection; early recognition, cultures before antibiotics when feasible, prompt broad-spectrum antimicrobials, and resuscitation drive outcomes
Empiric antimicrobial choice is guided by the likely pathogen and source, then narrowed (de-escalated) once culture and susceptibility data return
HIV is screened with combination antigen/antibody testing; antiretroviral therapy is recommended for essentially all diagnosed patients regardless of CD4 count
Healthcare-associated infections such as catheter-associated urinary tract infection and central line-associated bloodstream infection are largely preventable with device stewardship and hand hygiene
Infectious Diseases is 7% of the NCCPA PANRE blueprint, a meaningful share for a recertifying PA. Items reward syndromic reasoning: identify the likely source and pathogen, start rational empiric therapy, and adjust once data return. Prevention through immunization and infection control is also frequently tested.
Common Infections by Category
| Category | Representative Conditions | Practical Point |
|---|---|---|
| Bacterial | Community-acquired pneumonia, cellulitis, urinary tract infection, streptococcal pharyngitis | Source plus likely organism drives empiric drug choice |
| Viral | Influenza, COVID-19, mononucleosis, viral hepatitis, herpes/varicella | Most are supportive care; antivirals for selected pathogens or hosts |
| Fungal | Oral/vulvovaginal candidiasis, dermatophytes, invasive fungal disease in immunocompromised | Invasive disease concentrates in immunosuppression |
For common syndromes, the exam wants the typical pathogen and a reasonable first-line agent, plus when severity or host risk changes the plan.
Sepsis
Sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection; septic shock adds circulatory and metabolic derangement with persistent hypotension. Recertification content emphasizes early recognition and a bundle-style approach:
- Recognize infection plus organ dysfunction early.
- Obtain cultures before antibiotics when this does not delay therapy.
- Start broad-spectrum antimicrobials promptly.
- Resuscitate with fluids and reassess perfusion; add vasopressors for refractory hypotension.
- Identify and control the source.
Time to effective antimicrobial therapy is a major modifiable factor in outcomes.
HIV
Human immunodeficiency virus (HIV) screening uses a laboratory combination antigen/antibody (4th-generation) immunoassay, with confirmatory testing on reactive results. Routine opt-out screening is recommended broadly for adolescents and adults, with repeat testing for ongoing risk.
Current practice recommends antiretroviral therapy (ART) for essentially all people with HIV regardless of CD4 count, both for individual health and to reduce transmission. The CD4 count gauges immune status and opportunistic infection risk, while the viral load tracks treatment response, with durable suppression the goal. Pre-exposure prophylaxis (PrEP) is offered to people at substantial risk of acquiring HIV.
Antimicrobial Selection Principles
Good antimicrobial decisions follow a stewardship logic rather than reflexive broad coverage:
- Confirm infection rather than colonization or contamination; asymptomatic bacteriuria usually does not warrant antibiotics outside specific situations such as pregnancy.
- Cover the likely pathogens for the source and host, accounting for local resistance.
- De-escalate to the narrowest effective agent once cultures and susceptibilities return.
- Right duration and route, transitioning intravenous to oral when the patient is improving and able.
- Document allergies accurately, since unverified penicillin allergy labels push patients toward broader, less optimal agents.
Immunizations
Adult immunization is recurrently tested. PAs should know that recommendations are organized by age, condition, and risk and are issued through national advisory guidance updated periodically.
| Vaccine Theme | Typical Adult Consideration |
|---|---|
| Influenza | Annual vaccination for most adults |
| COVID-19 | Per current national recommendations |
| Td/Tdap | Periodic tetanus-containing booster; Tdap for pertussis protection |
| Pneumococcal | Recommended by age threshold and risk conditions |
| Zoster | Recommended for older adults per current schedule |
| Hepatitis B | Risk-based and broadened adult recommendations |
Verify exact ages and intervals against the current schedule rather than memorizing fixed numbers, since these are revised over time.
Healthcare-Associated Infections
Healthcare-associated infections (HAIs) are infections acquired during care delivery. High-frequency, largely preventable examples include catheter-associated urinary tract infection (CAUTI), central line-associated bloodstream infection (CLABSI), surgical site infection, and Clostridioides difficile infection. Core prevention is hand hygiene, device stewardship (insert only when indicated, remove promptly), aseptic technique, and isolation precautions. Antimicrobial stewardship limits resistance and C. difficile risk.
Exam Strategy
Map the syndrome to the likely pathogen, start rational empiric therapy, de-escalate with data, and treat prevention (vaccines, device removal, hand hygiene) as testable management, not background.
A 70-year-old with a urinary source presents with fever, tachycardia, hypotension, and an elevated lactate consistent with septic shock. Which sequence best reflects appropriate early management?
Delay antibiotics until all imaging is complete, then give a narrow-spectrum agent
Obtain cultures when feasible without delaying therapy, start prompt broad-spectrum antimicrobials, resuscitate with fluids, and pursue source control
Give antipyretics and observe for 24 hours before any antimicrobial therapy
Start a narrow oral antibiotic and discharge with outpatient follow-up
An asymptomatic adult is being screened for HIV. Which statement best reflects current testing and treatment principles?
Screening relies only on viral load, and treatment is deferred until CD4 falls below a fixed threshold
A combination antigen/antibody immunoassay is used for screening, and antiretroviral therapy is recommended for essentially all people with HIV regardless of CD4 count
HIV cannot be screened without symptoms, and therapy is only started after an opportunistic infection occurs
A single rapid antibody test is definitively diagnostic with no confirmatory testing needed
Which action best reflects antimicrobial stewardship after empiric therapy when culture and susceptibility results return showing a narrow-spectrum agent would be effective?
Continue the broadest agent indefinitely to avoid any risk
De-escalate to the narrowest effective agent and set an appropriate duration
Stop all antibiotics immediately regardless of clinical status
Add a second broad agent for redundancy
Sections you finish are checked off in the contents.